Spent mushroom substrate (SMS), a waste product from mushroom cultivation, in addition to being rich in essential nutrients for crop growth, contains actively growing mushroom mycelia and metabolites that suppress some plant pathogens and pests. SMS thus has potential for fostering the suppressiveness of soil-borne pathogens of farms. This study determined the potential of using the spent Pleurotus ostreatus substrate (SPoS) to suppress the plant-parasitic nematode Radopholus similis in bananas. R. similis is the most economically important nematode in bananas worldwide. The effect of SPoS on R. similis was assessed through two in vivo (potted plants) experiments between May 2023 and June 2024. Five-month-old East African highland banana (genome AAA) plantlets that are highly susceptible to R. similis were used. In the first experiment, the plantlets were established in 3 L pots containing (i) pre-sterilized soil, (ii) pre-sterilized soil inoculated with nematodes, (iii) pre-sterilized soil mixed with 30% (v/v) SPoS, (iv) pre-sterilized soil mixed with 30% (v/v) SPoS followed by nematode inoculation, (v) SPoS without soil, and (vi) SPoS without soil inoculated with nematodes. The SPoS was already decomposed; thus, it may or may not have contained active mycelia. The nematodes were introduced two weeks after the SPoS application. In the second experiment, SPoS was introduced two weeks after nematode inoculation. The SPoS treatments without soil were not evaluated in the second experiment. Both experiments were monitored over a three-month period. Each screenhouse treatment contained four plants and was replicated thrice. In the first experiment, data were collected on changes in soil nutrient content, below- and aboveground biomass, root deaths, root necrosis due to nematode damage, and R. similis population in root tissues and soil. In the second experiment, data were collected on root deaths and the number of nematodes in root tissues and the soil. The SPoS improved crop biomass yield, reduced root damage, and colonization by R. similis. The potential of SPoS to improve the management of R. similis and banana production under field conditions needs to be determined.

Compost tea is widely recognized for its beneficial effects on crop growth and soil health. However, its efficacy varies depending on the composition of the feedstock and brewing conditions. This study investigates the chemical composition and agronomic impact of compost tea prepared from a commercial mixture of plant residues and animal manure. Standard chemical analyses, combined with solid-state 13C CPMAS NMR spectroscopy, were employed to characterize the organic chemistry of the feedstock. High-throughput sequencing of bacterial and eukaryotic rRNA gene markers was used to profile the microbiota. Compost tea was applied to three crops, Allium cepa, Beta vulgaris, and Lactuca sativa, grown in protected Mediterranean environments on volcanic soils. The 13C CPMAS NMR analysis revealed that the feedstock is predominantly composed of plant-derived tissues, including grass straw, nitrogen-fixing hay, and animal manure, with a significant presence of O-alkyl-C and di-O-alkyl-C regions typical of sugars and polysaccharides. Additionally, the chemical profile indicated the presence of an aliphatic fraction (alkyl-C), characteristic of lipids such as waxes and cutins. The compost tea microbiome was dominated by Pseudomonadota, with Pseudomonas, Massilia, and Sphingomonas being the most prevalent genera. Compost tea application resulted in significant yield increases, ranging from +21% for lettuce to +58% for onion and +110% for chard. Furthermore, compost tea application reduced slug damage and enhanced the shelf life of lettuce. These findings highlight the bio-stimulant potential of this standardized compost tea mixture across different vegetable crops.